Refrigerating system with defrosting circuit



Aug. 10, 1954 E. w. ZEARFOSS, JR

REFRIGERATING SYSTEM WITH DEFROSTING CIRCUIT Filed Sept. 27, 1951 Patented Aug. 10, 1954 REFRIGERATING SYSTEM WITH DEFROST- ING CIRCUIT Elmer W. Zearfoss, J12, Philadelphia, Pa., assignor to Philco Corporation, Philadelphia, Pa, a corporation of Pennsylvania Application September 27, 1951, Serial No. 248,515

Claims. (Cl. 62-11755) The present invention relates .to refrigerating apparatus and, more particularly, to a refrigeration system of the type having provision for heating the evaporator to effect removal of frost which, during normal operation of the system, accumulates on the evaporator surfaces. Specifically, the invention has to do with improvements in defrosting systems wherein gaseous refrigerant is introduced into the evaporator and permitted to condense therein to sup-ply the necessary heat for melting the accumulated gaseous refrigerant within the evaporator, must be withdrawn from the latter and must be reevaporated before subjection to the pumping action of the compressor. Particular difficulties are encountered when attempts are made to provide simple means which is capable of adequately controlling the flow of refrigerant through the system to change from a normal refrigerating cycle to a defrosting cycle, and back to the normal refrigerating cycle, and which is further capable of working in accordance with those thermodynamic principles which must be respected in order to maintain the primary purpose of the system, namely, efficient refrigeration.

Various proposals have been made to solve and to overcome the above mentioned problems and difficulties. For example, it .has been suggested to provide a refrigeration system with valve-controlled conduit means designed to bypass the restrictor and to conduct gaseous refrigerant to the evaporator directly from the compressor or condenser. Another suggestion has been to provide a refrigeration system including a reservoir which, during a normal refrigerating cycle, serves to store a surplus quantity of liquid refrigerant and which is associated with heating means functioning during a defrosting cycle, to cause ebullition of the stored refrigerant, the resultin vaporized-or gaseous refrigerant being then permitted to flow through the evaporator. Systems provided with a Valving arrangement requires specially designed and accurately made and assembled valving means to insure reliability of operation in initiat ng and in terminating a defrosting cycle. As to those systems which have a reservoir for surplus refrigerant, it is generally necessary to provide an oversized motor-compressor to take care of the added refrigerant which circulates through the system during a defrosting cycle. Clearly, the use of specially designed and accurately made and assembled valves, as well as the use of an oversized motor-compressor, results in increasing the overall cost of the system and in complicating the operation of such a system.

It is an important object of the present invention to provide a simplified defrosting arrangement which can be readily associated with the evaporator circuit, which overcomes the hereinbefore stated problems and difficulties Without the use of valves and without necessitating an overcharge of refrigerant, and which requires a motor-compressor no larger than is necessary to obtain adequate efiicient refrigeration. Broadly, this objective and resulting advantages of the invention are realized by employing a simple auxiliary circuit which parallels the evaporator circuit, and by associating simple flow controlling means with said'circuits, said controlling means being operable temporarily to interrupt the normal flow of refrigerant to the evaporator and to bring about such a condition that gaseous refrigerant is caused to circulate through the auxiliary circuit to effect defrosting of the evaporator surfaces. A practicable embodiment of the invention includes a novel association of refrigerant distributing means, flow impeding means and heat generating means, all of said means cooperating to fulfill the requirements of efficient refrigeration, as Well as of adequate defrost.

The novel features of the invention and the manner in which the above recited and other objectives and advantages are best achieved, will clearly appear from the following description of the embodiment illustrated in the accompanying drawing, in which:

Figure 1 is a diagrammatic representation of a refrigeration systemembodying the present invention, and shows the condition which exists in the system during a normal refrigerating cycle, and

Figure 2 illustrates a part of the system represented in Figure 1, and shows the condition 3 which exists in the system during a defrosting cycle.

With more particular reference to the drawing, the illustrated embodiment comprises the usual elements of a refrigeration system of conventional type, namely, a compressor [0, a condenser H, and an evaporater circuit [2. This evaporator circuit defines a serpentine path for circulation of refrigerant in heat exchange relation with the customary evaporator body which is represented at 52a. The compressor, condenser and evaporator are connected in series flow circuit through the agency of suitable connections and conduits including a flow restrictor or capillary tube It which leads from the condenser, a feed line It which establishes communication between the outlet of said flow restrictor or capillary tube and the inlet of the evaporator, a header or accumulator it: which communicates with the outlet of the evaporator, and a suction line It which connects said header or accumulator with the inlet side of the compressor housing. As is customary, a portion of the capillary tube and a portion of the suction line are advantageously associated in heat exchange relation, as is represented at ll.

In addition to the above mentioned usual components, the system according to the present invention, includes a refrigerant distributing chamber i8 and a second restrictor it. The distributing chamber is in open communication with the capillary tube it and with the feed line it, said capillary tube being connected with an upper portion of said chamber through a suitable feed connection Md, and said feed line being connected, as at Mb, to lead from a lower portion of said chamber. The second restrictor i9 is incorporated in the feed line between said chamber and the evaporator and, in the illustrated embodiment, is made of capillary tubing.

Also, in accordance with the invention, the system includes an auxiliary or defroster circuit 2%! which parallels the evaporator circuit 52 and which is arranged in heat exchange relation with the evaporator body 1201,. The auxiliary circuit is supplied with restrictors 2i and '22 which are disposed at the inlet and outlet portions, respectively, of said auxiliary circuit and which, in the illustrated embodiment, are also made of capillary tubing. As shown at 2c, the inlet end of the auxiliary circuit is connected in open communication with an upper portion of the distributing chamber, that is, at a point above the connection between said chamber and the feed line M. As shown at 2%, the outlet end of the said auxiliary circuit is connected to and communicates with the suction line it. A portion adjacent said outlet end of the auxiliary circuit is arranged in heat exchange relation, as is shown at 25, with a portion of the feed line, and another portion of this feed line is advantageously disposed in proximity to a portion adjacent the inlet end of the auxiliary circuit so that each of said last-named two portions is conveniently associated in heat exchange relation with a suitable heat generating element, such as electrical heater 26 which may be energized in response to actuation of any suitable known type of switching device 2?.

Referring now to Figure 1, it will be seen that during a normal refrigerating cycle, the heater 26 is de-energized so that it has no effect in the system. Under this condition, hot gaseous refrigerant is delivered from the compressor to the condenser where the compressed refrigerant gives up heat to the ambient air and is converted to liquid state. From the condenser, liquid refrigerant passes through the main restrictor it Which subjects the refrigerant to a pressure reduction and partial change of state so that the refrigerant entering the chamber [8 is in the form of a mixture of liquid and gas. In chamber Hi, the liquid gravitates to the lower portion of the chamber and thus separates itself from the gas which occupies the upper portion of said chamber. The liquid passes directly out of the chamber through feed line Hi and through second restrictor l9 and into the evaporator circuit I2 where the refrigerant vaporizes and, in the process, absorbs heat from the ambient air. Heatladen vaporized refrigerant which accumulates in the header or accumulator i5, is withdrawn through the suction line IE into the compressor [0.

During the above described refrigerating cycle, it is desirable that the restrictor l9 handle only liquid refrigerant and, for that purpose, the restrictors l9 and 2! are so related with respect to each other that the feeding of liquid from the chamber H; to the evaporator circuit i2 through the restrictor I9, and the escape of gas from said chamber into the auxiliary circuit 2t through the restrictor 2|, occur in such a manner as to insure the presence of liquid in said chamber in a sufficient quantity to provide an effective trap against the passage of gas into the feed line it.

It will be recognized that the restrictor 22 (located at the outlet end portion of the auxiliary circuit 20) is apt to so restrain the gas within said auxiliary circuit as to cause the pressure in said auxiliary circuit to rise above the pressure which is maintained in the evaporator circuit 12, with the result that the saturation temperature of the refrigerant in said auxiliary circuit is higher than the saturation temperature of the refrigerant in said evaporator circuit. Because of this difference in saturation temperature, the liquid refrigerant in the evaporator circuit [2 will absorb heat from the gaseous refrigerant in the auxiliary circuit 26 and, thus, will effect condensation of said gas in said auxiliary circuit. Ordinarily, this condensing effect would represent a loss of refrigeration. However, according to the invention, this loss is recovered by the fact that liquid refrigerant passing out of the restrictor 22 at suction pressure, is put in heat exchange relation, at 25, with the higher pressure refrigerant passing through the feed line M. This heat exchange causes the liquid from the auxiliary circuit to vaporize and, in the process, to subcool the liquid fed to the evaporator to a sufficient degree to maintain the evaporator within the proper refrigerating temperature range While taking up heat from the refrigerant in the auxiliary circuit.

When it becomes desirable or necessary to defrost the evaporator, the heater 26 is energized. Heat dissipated by said heater causes vaporization of liquid refrigerant in the feed line is and ahead of the restrictor l9. Thus, as long as the heater is kept in operation, gas is continuously maintained at the restrictor I!) so that its effective restriction is materially increased. As a result, liquid rises in the chamber 18, as is illustrated in Figure 2, and flows through the restrictor 2i and into that portion of the auxiliary or defroster circuit which is in heat transfer relation with the heater. In passing through said heated portion of the auxiliary circuit, the refrigerant is converted into hot gas and, as such, continues to flow into the portion of the auxiliary circuit which is in heat exchange relation with the evaporator. In this latter portion of the auxiliary circuit, the gaseous refrigerant condenses thus providing the necessary heat for melting the frost accumulated on the evaporator surfaces. The refrigerant which is thus condensed, flows out through the restrictor -22 for ultimate return to the compressor. It is of importance to note that because the quantity of refrigerant present in the suction line side of the heat exchange arrangement 25 greatly exceeds the quantity of refrigerant trapped in the feed line l4, said heat exchange arrangement no appreciable effect on the operation of the systern during the defrost cycle. Accordingly, liquid refrigerant which emerges from the restrictor 22, spills down the suction line and into the compressor housing and vaporizes at the prevailing suction pressure.

It is emphasized that the restrictor 22 constitutes a most significant part of the system as shown, especially insofar as concerns the defrosting cycle. As was hereinbefore indicated, because of the inclusion of the restrictor 22, the pressure in the auxiliary or defroster circuit 20 is elevated and maintained at a higher level than the pressure existing in the evaporator circuit i2, so that the saturation temperature of the refrigerant in said auxiliary or defroster circuit is above the saturation temperature of the refrigerant in said evaporator circuit. This feature of the invention makes it possible to satisfy the thermodynamic requirements necessary for adequate operation of the system, as will be presently described. During the defrost cycle, the greater part of the heat energy dissipated by the heater is absorbed by the refrigerant which passes into the defroster circuit. This is because the heater, with reference to the direction of flow, is placed ahead of restrictor tube IS in the evaporator circuit i2 and after the restrictor tube 21 in the defroster circuit 20 and, further, because the division of heat energy between said two circuits is effected largely by the resultant flow characteristic in the respective circuits. To put it in other words, it will be understood that comparatively little heat energy is required to establish and to maintain the vapor lock condition at the restricter i9, so that most of the heat energy dissipated by the heater is available to the refrigerant passing into the defroster circuit. Accordingly, during operation of the system, the refrigerant in the defroster circuit has a higher heat content than the refrigerant in the evaporator circuit, and since the refrigerant in the evaporator circuit is at lower saturation temperature than the refrigerant in the defroster circuit, this last mentioned refrigerant can reject heat to the frost and to the refrigerant in the evaporator circuit. Thus, the restrictor 22 provides effective means to establish the pressure-temperature gradient required to condense the refrigerant in the defroster circuit following the vaporization of said refrigerant in the circuit portion which is in heat exchange relation with the heater 26.

It is also important to note that because the restrictor 22 acts to maintain a higher pressure in the defroster circuit than in the suction side of the system, it is possible, during the defrosting cycle, to operate the defroster circuit at temperatures above the freezing point of water While the suction side of the system operates at temperatures below said freezing point. This mode of operation has the advantage that the compressor is not burdened with the high load which would be imposed upon it if it had to work at temperatures above freezing. Another advantage which resultsfrom the above described arrangement, is that the temperature of the defroster circuit can be elevated considerably above the freezing point of Water without deleteriously affecting the operation of the system. For that reason, the invention makes possible the presence of ample heat, in the defroster circuit, for transference to all parts of the evaporator.

When the defrost cycle is completed the heater is deenergized and, since the restrictor l 9 is then no longer vapor locked, liquid refrigerant is again free to flow into the evaporator circuit. As a result, the level of the refrigerant in chamber is drops, and the refrigerating condition, illustrated in Figure 1, is r e-established.

By way of example, it may be here stated that in a representative system which has yielded good results, the main restrictor l3 comprised 8 feet of tubing having an inside diameter of 0.031 inch, the restrictor is comprised 1 foot of tubing having an inside diameter of 0.031 inch, the restrictor 2i comprised 6 inches of tubing having an inside diameter of 0.031 inch, and the restrictor 22 comprised 3 inches of tubing having an inside diameter of 0.031 inch. With a system provided with restrictors having the above noted characteristics, it was found that 60 watts adequately established and maintained the vapor lock condition, so that by using a heater rated at 460 watts, then 340 watts were made available to the refrigerant entering the defroster circuit. This quantity of heat represents a dissipation of approximately 26 B. t. u.s per minute so that the period of time required to defrost, under normal conditions, is comparatively short. Of course, it is to be understood that the above noted values of the various components can be modified without losing the characteristic features and advan tages of the invention, so long as the stated proportions are reasonably observed.

From the foregoing description, it will be appreciated that the present invention provides a defrostable refrigerating system which is characterized by unusual constructional simplicity and operational reliability. Especially, it will be appreciated that the particular construction of the defroster circuit and its novel association in the system are significant features of the invention, and that these features make it possible effectively to control the refrigerating and defrosting operations without the utilization of intricate and costly mechanical means.

I claim:

1. In a defrostable refrigeration system of the type having a compressor, a condenser, an evaporator and conduit means including feed and suction lines connecting the compressor, condenser and evaporator in series flow circuit, a refrigerant distributing chamber interposed in the feed line, an auxiliary circuit having its inlet and connected with said chamber and its outlet end connected with the suction line, said auxiliary circuit including a portion arranged in heat exchange relation with the evaporator, a first restrictor located in the feed line between the condenser and said chamber, a second restrictor located in the feed line between said chamber and the evaporator, a third restrictor located in the auxiliary circuit between said chamber and the mentioned portion of said auxiliary circuit, a fourth restrictor located in the auxiliary circuit between the mentioned portion of said auxiliary circuit and the suction line, and heat generating means operable at selected times and disposed in heat exchange relation with the feed line be tween said chamber and said second restrictor and with the auxiliary circuit between said third restrictor and the mentioned portion of said auxiliary circuit.

2. A defrostable refrigerating system comprising an evaporator body, a pair of refrigerant circulating circuits, each provided with a portion arranged in heat exchange relation with said body, a condenser, refrigerant distributing means connected with said condenser and with said circuits and normally delivering liquid refrigerant from said condenser to one of said circuits, and flow modifying means associated with said circuits between said distributing means and said portion of each of said circuits, for interrupting delivery of liquid refrigerant to said one of said circuits from said condenser through said distributing means, for initiating a flow of liquid refrigerant to the other of said circuits from said condenser through said distributing means, and for converting to gas the liquid refrigerant flowing into said other of said circuits prior to entering said portion of said other of said circuits.

3. A defrostable refrigerating system comprising an evaporator body, a pair of refrigerant circulating circuits arranged in parallel relation with respect to each other, each of said circuits having a portion arranged in heat exchange relation with said body, a refrigerant condenser, a conduit for feeding liquid refrigerant from said condenser, said conduit being connected with said circuits and normally delivering liquid refrigerant from said condenser to one of said circuits, and flow modifying means associated with said circuits between their said portion and their connection with said conduit, for interrupting delivery of liquid refrigerant to said one of said circuits from said condenser through said conduit, for initiating a flow of liquid refrigerant to the other of said circuits from said condenser through said conduit, and for converting to gas the liquid refrigerant flowing into said other of said circuits prior to entering said portion of said other of said circuits.

i. In a defrostable refrigerating system of the type having a compressor, a condenser, an evaporator and conduit means including feed and suction lines connecting the compressor, condenser and evaporator in series flow circuit, the combination of a refrigerant distributor interposed in said feed line to receive liquid refrigerant from said condenser and normally delivering said liquid refrigerant to said evaporator, an auxiliary circuit provided with a portion arranged in heat exchange relation with said evaporator and having its inlet end connected with said distributor and its outlet end connected with said suction line, and flow modifying means associated with said feed line and with said auxiliary circuit between said distributor and said portion of said auxiliary circuit, for interrupting delivery of liquid refrigerant to said evaporator from said condenser through said distributor, for initiating a flow of liquid refrigerant to said auxiliary circuit from said condenser through said distributor, and for converting to gas the liquid refrigerant flowing into said auxiliary circuit prior to entering said portion thereof.

5. A defrostable refrigerating system comprising an evaporator body, a pair of refrigerant circulating circuits, each having a portion arranged in heat exchange relation with said body, refrigerant feeding means including a refrigerant distributor communicating with said circuits, heat generating means disposed in heat exchange relation with said circuits between said distributor and said portion of each of said circuits, 2. restrictor included in one of said circuits between said distributor and said heat generating means, and another restrictor included in the other of said circuits between said heat generating means and said portion of said other of said circuits.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,323,511 Baker July 6, 1943 2,526,032 La Porte Oct. 17, 1950 2,554,848 Warren May 29, 1951 2,611,587 Boling Sept. 23, 1952 

